Conventional belt retractors comprise a frame, in which a belt spool is rotatably mounted, locking teeth and a locking catch which can be brought from an initial position into a locking position by a locking mechanism, whereby the belt spool is locked relative to the locking teeth.
In addition to the usual function of a belt retractor, namely making available a safety belt and blocking the unwinding of the belt webbing from the belt spool if required, many belt retractors nowadays also make available a so-called force-limiting function. The force-limiting function consists in making possible an unwinding of the belt webbing, despite the belt spool actually being locked, when the force acting in the belt webbing exceeds a predetermined value. The unwinding of the belt webbing which is then possible leads to an additional way being made available for decelerating the vehicle occupant, whereby the forces occurring due to the acting deceleration are reduced. In this way, the forces due to deceleration can be limited to a value where usually no injuries of any kind occur to the occupant of the vehicle.
The force-limiting function can be achieved for example by means of a torsion rod which acts between the belt spool and the locking teeth, which are arranged on the belt spool.
The object of the invention consists in providing a belt retractor in which the force-limiting function can be realized with a low expenditure in terms of construction. Additionally, the limit of the torque acting on the belt spool, from which up the force-limiting function starts becoming effective, can be adapted easily to the respective requirements.